Antagonism of TRPV4 channels partially reduces mechanotransduction in rat skeletal muscle afferents.

Mechanical distortion of working skeletal muscle induces sympathoexcitation via thin fibre afferents, a reflex response known as the skeletal muscle mechanoreflex. However, to date, the receptor ion channels responsible for mechanotransduction in skeletal muscle remain largely undetermined. Transient receptor potential vanilloid 4 (TRPV4) is known to sense mechanical stimuli such as shear stress or osmotic pressure in various organs. It is hypothesized that TRPV4 in thin-fibre primary afferents innervating skeletal muscle is involved in mechanotransduction. Fluorescence immunostaining revealed that 20.1 ± 10.1% of TRPV4 positive neurons were expressed with DiI-labeled small dorsal root ganglia (DRG) neurons, and 9.5 ± 6.1% of TRPV4 were co-localized with C-fibre marker, peripherin-positive neurons. In vitro whole-cell patch clamp recordings from cultured rat DRG neurons demonstrated that mechanically-activated current amplitude was significantly attenuated after the application of the TRPV4 antagonist, HC067047 compared to control (P = 0.004). Such reductions were also observed in single-fibre recordings from a muscle-nerve ex vivo preparation where HC067047 significantly decreased afferent discharge to mechanical stimulation (P = 0.007). Likewise, in an in vivo decerebrate rat preparation, the renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to passive stretch of hindlimb muscle were significantly reduced by intraarterial injection of HC067047 (ΔRSNA: P = 0.019, ΔMAP: P = 0.002). The findings suggest that TRPV4 plays an important role in mechanotransduction contributing to the cardiovascular responses evoked by the skeletal muscle mechanoreflex during exercise. KEY POINTS: Although a mechanical stimulus to skeletal muscle reflexively activates the sympathetic nervous system, the receptors responsible for mechanotransduction in skeletal muscle thin fibre afferents have not been fully identified. Evidence suggests that TRPV4 is mechanosensitive channel that plays an important role in mechanotransduction within various organs. Immunocytochemical staining demonstrates that TRPV4 is expressed in group IV skeletal muscle afferents. In addition, we show that the TRPV4 antagonist, HC067047, decreases the responsiveness of thin fibre afferents to mechanical stimulation at the muscle tissue level as well as at the level of dorsal root ganglion neurons. Moreover, we demonstrate that intraarterial HC067047 injection attenuates the sympathetic and pressor responses to passive muscle stretch in decerebrate rats. These data suggests that antagonism of TRPV4 attenuates mechanotransduction in skeletal muscle afferents. The present study demonstrates a probable physiological role for TRPV4 in the regulation of mechanical sensation in somatosensory thin fibre muscle afferents. Abstract figure legend Blocking transient receptor potential vanilloid 4 (TRPV4) channels has an inhibitory effect on sympathetic and pressor responses to mechanical stimulation by attenuating mechanotransduction in sensory afferents innervating skeletal muscle. The TRPV4 antagonist, HC067047, reduces the responsiveness of thin fibre muscle afferents and small dorsal root ganglion neurons to mechanical stimulation. Furthermore, it is demonstrated that intraarterial injection of HC067047 suppresses the sympathetic nerve activity and blood pressure responses to passive hindlimb muscle stretch in vivo. These findings suggest that TRPV4 may play a crucial role in mechanotransduction contributing to the cardiovascular responses evoked by the skeletal muscle mechanoreflex during exercise. Design made in BioRender. This article is protected by copyright. All rights reserved.